1. Field of the Invention
The present invention relates to a drum for an image recording apparatus, and more particularly to a drum for an image recording apparatus capable of absorbing an image recording material and winding the thus-absorbed image recording material on the outer surface thereof.
2. Description of the Related Art
In an image scanning and recording apparatus, a recording material is wound to a rotary drum capable of absorbing the recording material and the image is scanned by a relative movement between a recording head disposed to correspond to this rotary drum and the recording material so that the recording material is exposed to light. After the recording material has been exposed to light, it is removed from the rotary drum so as to be sent to the ensuing processes.
As shown in FIGS. 12 and 13, the rotary drum above is structured in such a manner that hollow shafts 172 and 175 are, with side plates 173, secured to the two ends of the cylindrical main body 170 thereof.
As shown in FIG. 14, an wedge shape cutout 176 is formed in a portion of the outer surface of the main body 170. Furthermore, a plurality of absorption holes 174 are formed on the outer surface of the main body 170, this absorption hole 174 being also formed in the cutout 176. A guide plate 178 is so disposed above the cutout 176 so as to cover this cutout 176, this guide plate 178 acting to guide the recording material to the cutout 176.
The shaft 172 for the rotary drum is supported by a housing and is connected to a vacuum source via a connection hole formed in the housing, the shafts 175 being further connected to a power source for the rotation.
The recording material is wound to the outer surface of the drum in such a way that the recording material is supplied along the outer surface of the main body 170, and the front end of the recording material is inserted into a gap formed between the cutout 176 and the guide plate 178. Then, air in the main body 170 is sucked via the shaft 172 so that a negative pressure is generated. As a result, the front end of the recording material is brought into close contact with the absorption holes 174. Furthermore, the recording material is brought into close contact with the outer surface of the drum with the rotary drum rotated by the rotating power.
The rotary drum is, as shown in FIG. 15, manufactured from a plurality of manufacturing processes. That is, the main body 170 is cut from a pipe in a cutting process 180. In a lathe process 182, the two ends of the thus-cut main body 170 are subjected to a fitting work. On the other hand, the side plates 173 and the shaft 172 are manufactured from the raw material in lathe processes 184 and 186, and the thus-manufactured side plates 173 and the shaft 172 are integrated with each other in a press fitting process 188. Then, the side plates 173 to which the shaft 172 has been secured are press-fitted into the main body 170 so that they are integrated with each other before being subjected to cutting in a milling process 192. Then, the absorption holes are formed in the outer surface of the main body in a milling process 194 before being further subjected to a lathe process 196 so that the outer surface is finished so as to become a smooth surface. Then, the guide plate is finally secured as described above.
As described above, since the conventional rotary drum is manufactured from a considerably large number of manufacturing processes, the manufacturing work is too complicated and a long time needs to be taken to complete the manufacturing. Furthermore, the lathe work and the milling need expensive machines, causing the manufacturing cost to become excessively high. Furthermore, each of these multiplicity of manufacturing processes needs to be subjected to a checking for the manufacturing accuracy, causing the necessity of employing skilled workers.
Since the conventional rotary drum is arranged such that the front end of the recording material supplied as described above is guided by the guide plate 178, the thus-guided recording material is simply inserted into the gap formed between the cutout 176 and the guide plate 178. Therefore, the thus-inserted recording material can easily float toward the guide plate 178 due to the rigidity thereof. As a result, if a negative pressure is generated by sucking air, the front end of the recording material cannot be assuredly brought into contact with the absorption holes 174. In particular, if the front end of the recording material has curl or turn, the problem of the type described above becomes excessively apparent.
Furthermore, if the recording material is inserted by an excessive length into the gap formed between the cutout 176 and the guide plate 178, sucked air leakage can be generated due to the buckling of the front end of the recording material in this gap.
As a result, the performance of absorbing the recording material deteriorates, causing a problem in that the recording material cannot be assuredly wound to the rotary drum to arise.
In order to overcome the above-described problems, it needs to take countermeasures against them in such a way that the shape of cutting the front end of the recording material and the positioning of the same are made properly or that the feeding control of the front end of the recording material can be conducted precisely. In addition, all of the above-described method arise the cost excessively.
Furthermore, since air is sucked via the shaft 172 in the conventional rotary drum, the portions bearing the rotation of the shaft 172, that is, the space between the outer surfaces of the rotating shaft 172 and the housing necessarily encounters a problem of sucked air leakage. Therefore, a problem arises in that the recording material cannot be brought into assuredly contact with the outer surface of the main body 170 or another problem arises in that the necessary power for operating the negative pressure source cannot be reduced.
In order to overcome the above-described problems, the applicant of the present invention has disclosed an art established for the purpose of preventing sucked air leakage by a so-called "labyrinth effect" generated due to an extremely narrow slit (several tens of microns) formed between the outer surface of the shaft 172 and the housing for a distance of several tens of millimeters (Japanese Patent Laid-Open No. 62-214768).
According to this disclosure, the small gap formed between the outer surfaces of shaft 172 and the housing can generate an effect similar to the labyrinth effect so that any sucked air leakage through the portions bearing the rotation of the shaft 172 can be prevented. In addition, since the outer surface of the shaft 172 cannot be brought into contact with the housing, the frictional resistance in this area can be reduced, and the power needed to operate the rotating power source can be reduced.
However, the gap formed between the outer surface of the shaft 172 and the housing is extremely small (substantially several tens of microns) and this gap is positioned in a considerably wide region in the bearing structure for the shaft 172, an extreme accurate machining needs to be conducted to manufacture the shaft 172 and the housing. Therefore, the manufacturing yield is insufficient and the cost becomes excessively high. Furthermore, a complicated adjustment needs to be conducted when the above-described two types of components are assembled to each other. In addition, if a slight warp of the shaft 172 due to an impact is generated, an operative malfunction can occur due to the interference with the housing. Therefore, it is necessary to pay attention during handling the above described structure and during usage.
To this end, an object of the present invention is to provide a rotary drum capable of being manufactured from simple and reduced number of manufacturing processes with its cost reduced.
Another object of the present invention is to provide a rotary drum in which a recording material can be assuredly and stably absorbed and wound to the outer surface thereof with its cost reduced.
Another object of the present invention is to provide a sheet absorption drum in which any sucked air leakage can be prevented when internal air is sucked via shaft which is rotatably supported with a simple structure, causing the manufacturing yield to become significantly high, and causing the required cost to be reduced.